WASHINGTON (AP) -- It's so easy to fabricate the medical certificates required to operate commercial trucks on the nation's highways that there's almost no incentive for truckers to obtain a legitimate document, according to a congressional study.

The House Transportation and Infrastructure Committee's study -- expected to be released at a hearing Thursday -- found so few controls over how drivers obtain medical certificates that it's "relatively easy for a motivated commercial driver to circumvent the physical examination requirement." Nor is there any database or central repository which would allow state inspectors to verify the legitimacy of a medical certificate.

"Because so few attempts are made to authenticate a certificate, there is little risk that a driver will be caught if he or she forges or adulterates a certificate," according to the report, which was obtained by The Associated Press.

The Transportation Committee's study was based on a sample of 614 medical certificates obtained from truck drivers at roadside inspections in California, Illinois and Ohio. The committee's staff attempted to contact the examiners named on the medical certificates but could only verify 407 as valid.

One Ohio doctor contacted by the committee said forgery of medical certificates is so commonplace "no one gets alarmed by it anymore."

The committee called officials of the Federal Motor Carrier Safety Administration to explain at the hearing why the agency has doubts about the safety of the nation's highways. They identified more than 1,000 drivers with vision, hearing or seizure disorders, which generally would prohibit a trucker from obtaining a valid commercial license.

Truckers violating federal medical rules have been caught in every state, according to an AP review of 7.3 million commercial driver violations compiled by the Transportation Department in 2006, the latest data available. Texas, Maryland, Georgia, Florida, Indiana, Pennsylvania, Illinois, Michigan, Alabama, New Jersey, Minnesota and Ohio were states where drivers were sanctioned most frequently for breaking medical rules, such as failing to carry a valid medical certificate. Those 12 states accounted for half of all such violations in the United States.

(Copyright 2008 by The Associated Press.  All Rights Reserved.)